This application claims the priority of German Application No. 199 06 148.3 filed Feb. 13, 1999, which is incorporated herein by reference.
This invention relates to a fiber tuft feeder particularly for a carding machine, a roller card unit, a cleaner or the like. In particular, the invention concerns a device for charging a chute of the feeder with fiber tufts delivered by a transporting air stream into the chute. The fiber tufts are withdrawn from the chute at another location thereof. A separation of the transporting air stream from the fiber tufts is effected by an air-pervious surface through which the separated transporting air stream enters into an after-connected exhaust air unit which has an exhaust air chamber provided with a valve, such as an adjustable closing element.
European patent document 0 176 668, to which corresponds U.S. Pat. No. 4,878,784, discloses a device for pneumatically charging a chute from the top with fiber tufts which are removed from the chute by a withdrawing roll pair situated at the chute bottom. The device further has an exhaust air chamber which is separated from the chute by an air-pervious chute wall. The exhaust air chamber is connected with an exhaust air conduit by means of an opening in an otherwise impervious wall portion. A shutoff gate cooperates with the opening and is movable into a selectable, partially blocking position for varying the resistance to the air stream passing through the opening. In operation the entire volume of air separated from the fiber tufts passes through the air-pervious wall into the exhaust air chamber. Conventionally, low pressures prevail behind the air-pervious chute wall. By virtue of the higher charging pressure in the chute, differential pressures are obtained which may cause high flow velocities through the air-pervious chute walls. Such high velocities result in a lap formation with satisfactory width distribution and compression. Lap formation begins immediately where the air is capable of exiting the chute and the fiber tufts are entrained by the high-speed air flow and impact on the air-pervious surface. The air stream automatically guides larger fiber tuft quantities to a location where the material column in the chute is the shallowest because the resistance to the air flow is the lowest there. In fractions of a second the air flow equalizes differences in the height level of the tuft column over the entire width of the feed chute and thus an excellent uniformity of the fiber lap over the entire chute width is obtained.
Since the fiber lap is very intensively compressed aerodynamically over a small height difference, the air-pervious chute wall contributes only very little to the outflow of air below the upper level of the material mass. Disadvantageously, through the resulting, significantly reduced air outlet surface only a very small air quantity may exit and contribute to the lap formation. It is a further disadvantage that the air quantities required for the fiber transport are significantly greater than what would be needed for an optimal lap formation. Problems may be encountered particularly in case of large outputs in which partially significantly higher air transport quantities are required. The increased air transport quantity exceeds the air quantity required for the lap formation and clogging may result which prevents lap formation and causes operational disturbances.
It is an object of the invention to provide an improved device of the above-outlined type from which the discussed disadvantages are eliminated, which, in particular, permits the use of increased transport air quantities and which makes possible in a simple manner an undisturbed lap formation.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the fiber tuft feeder includes a chute, a first air-pervious surface forming part of the chute wall and a first exhaust air chamber adjoining the first air-pervious surface externally of the chute. The first exhaust air chamber is in a pneumatic communication with the chute through the first air-pervious surface. A device charges the chute with an air stream carrying fiber tufts. A first part of the air stream is separated from the fiber tufts by, and passing through, the first air-pervious surface into the first exhaust air chamber whereby a fiber tuft column is formed in the chute in the region of the first air-pervious surface. A second air-pervious surface forms part of the chute wall and is situated upstream of the first air-pervious surface. A second exhaust air chamber adjoins the second air-pervious surface externally of the chute and is separate from the first exhaust air chamber. The second exhaust air chamber is in a pneumatic communication with the chute interior through the second air-pervious surface for receiving a second part of the air stream. An air outflow opening is provided in a wall of the second exhaust air chamber and an adjustable valve cooperates with the air outflow opening for varying a flow passage area thereof.
By means of the additional (second) air-pervious surface one part of the tuft-transporting air stream in the chute is separated from the fiber tufts already above the (first) air-pervious surface associated with the fiber tuft column. By integrating the additional air-pervious surface in the chute region, a subsequent fiber tuft transport is enhanced by gravity. By virtue of the adjustability of the air outlet of the upper (second) exhaust air chamber, the differential pressure may be maintained small at the additional air-pervious surface (sieve, perforated plate or comb), while the outlet surface is maintained constant. The pressure in the second exhaust air chamber is increased by throttling until the desired air quantity flows to the lower-lying air-pervious surface. In this manner, a stepped air outlet in chute sections of different height may be set. At the same time, the measures according to the invention make possible an increased output with undisturbed fiber lap formation.
The invention has the following additional advantageous features:
The air-pervious surface associated with the deposited fiber tufts (first air-pervious surface) is adjoined by an independent exhaust air chamber.
The valve is adjoined by an exhaust air channel.
Both exhaust air chambers are coupled to the exhaust air channel.
The counter pressure in the exhaust air chamber adjoining the second air-pervious surface can be set by the adjustable valve which may be an adjustable throttle slide and which may be set as a function of the volume of the transporting air stream.
At least two second air-pervious surfaces are provided in respective opposite chute walls.
At least two second air-pervious surfaces are provided which extend throughout the width of the respective chute wall.
The second air-pervious surfaces are situated side by side.
A displaceable closure element is provided which may open or close at least two air outflow openings and which may be movable in a horizontal direction.
The displaceable closure element has air passage openings and blocking elements for controlling the air outflow openings.
The displaceable closure element has blocking surfaces for the air outflow openings.
The displaceable closure element permits a simultaneous shift of the blocking elements and the air passage openings.
The air outflow openings and the air passage openings have unlike shapes; the air outflow openings are rectangular or quadratic and the air passage openings have other polygonal shapes.
The air passage openings are triangular or trapezoidal.
The distance between the air outflow openings is uniform.
The shape of the air passage openings is different.
The free surface of the air outflow openings is so configured that over the entire width of the chute a uniform transport air stream is obtained.
The chute is the reserve chute of a fiber tuft feeder and a feed chute adjoins the reserve chute downstream thereof.
At the lower end of the reserve chute a tuft advancing assembly is arranged which has a rapidly rotating opening roll.
The distance between the air passage openings is uniform.